This is the first competing continuation of a proposal that was aimed at the development of a new non-invasive brain imaging method, the event-related optical signal (EROS). The purposes of this continuation are (a) to further extend the development of this method and knowledge about its spatial and temporal resolution in a systematic and parametric fashion, and (b) to compare and integrate it with other existing electrical and hemodynamic brain imaging techniques (the event-related brain potential, or ERP, and functional Magnetic Resonance Imaging, or fMRI). Functional brain imaging methods are becoming a central tool in the study of brain function, and have a number of potential applications in neurology, psychiatry, aging research, etc. However, presently available techniques emphasize either spatial or temporal resolution. This separate emphasis on temporal or spatial information does not always provide an accurate depiction of the rapid interactions between brain areas that are likely to underlie most complex brain functions. Work conducted during the initial funding period has established that EROS possesses a unique combination of spatial and temporal specificity. In addition, EROS can be interfaced with other techniques emphasizing spatial (such as fMRI) or temporal resolution (such as the ERP) to increase further the quality of the spatial and temporal information available to the investigator. The specific aims of this proposal are related to the practical development of this imaging approach as a tool in the study of brain function. They include answers to the following questions: (A) How specific and accurate are the estimates of the time course of activity in a particular cortical area obtained with EROS? (B) What are the minimum temporal and spatial separations between the activities in different areas that are discriminable with EROS? (C) Can EROS be used to detect patterns of correlation and coherence between the activity in different areas?